The Halogens
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Transcript of The Halogens
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Property Fluorine Chlorine Bromine Iodine
State at room temp Gas
Formula of molecule
Boiling point -188 °C –34 °C 59°C 184°C
Colour of vapour Pale yellow
Electronic configuration [He] [Ne] [Ar] [Kr]
The Halogens
Complete this table. Can you explain the trend in boiling point?
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Property Fluorine Chlorine Bromine Iodine
State at room temp Gas Gas Liquid Solid
Formula of molecule
F2 Cl2 Br2 I2
Boiling point -188 °C –34 °C 59°C 184°C
Colour of vapour Pale yellow Yellow/green Brown Black
Electronic configuration [He]2s2 2p5 [Ne] 3s2 3p5 [Ar] 4s2 3d104p5 [Kr] 5s2 4d105p5
The Halogens
Complete this table. Can you explain the trend in boiling point?
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Explaining the trend in boiling point
Temporary dipole occurs in one molecule owing to an unequal distribution of the electron cloud around it.
This temporary dipole induces a dipole in another molecule and the two attract each other.
Known as induced dipole-dipole forces or Van der Waals forces.
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The strength of van der waals forces increase:
The larger the molecule (due to a larger electron cloud)
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DISPLACEMENT REACTIONS
2KCl + I2
2KBr + I2
halogen
chlorine
bromine
iodine
salt (aq)potassium
chloridepotassium
iodidepotassiumbromide
2KCl + Br2
no reactionno reaction
no reaction
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The Halogens: Recognising them
• The halogens form solutions with different colours. A colour change will show if a reaction has taken place.
Halogen Water Cyclohexane
Cl2 Pale-green Pale-green
Br2 Orange Orange
I2 Brown violet
If you shake the reaction mixture with an organic solvent it can help distinguish between them
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What is the trend in reactivity of the halogens?
How can we explain this trend?
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The halogens get less reactive as we descend the group.
This is because…
- atomic size- shielding- nuclear attraction
How does this link to redox?
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Displacement: a redox reaction
Write an equation for the reaction between chlorine and bromide ions,
showing the changes in oxidation numbers.
Which species is the oxidising agent?
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Cl2 (aq) + 2Br- (aq) 2Cl- (aq) + Br2 (aq)0 -1 -1 0
Chlorine is reducedBromine is oxidised
Chlorine acts as an oxidising agent
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TRENDS IN OXIDISING ABILITY
Halogens react by gaining electrons
This means they are oxidising agents
They themselves are reduced
O xidationI sL osingR eductionI sG aining
Cl2 + 2e- 2Cl-
Gain of electrons
Oxidising ability of halogens decreases down the group
Because atoms become larger (and less electronegative)
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Oxidising power trend: Cl2 > Br2 > I2
When a halogen acts as an oxidising agent, it gains electrons (taken from the oxidised species).
X2 + 2 e- → 2 X-
Going down the group it becomes harder to gain an electron because:Atoms are larger & there is more shielding (due to extra electron shell)
Cl
Br
I